The present invention relates to a (hand) drilling tool, in particular it relates to a cutting tool made of hard metal with several (at least two) cutters for an element or more elements jointed therebetween of composite materials:                CFRP (Carbon Fiber Reinforced Plastic) composite material        
Such tool results to be suitable even for drilling (widening) in presence of pilot hole of:                light alloys (aluminium)        titanium alloys.        
In the aviation manufacturing industry, the assembly method has been performed for more than 50 years by the procedures of:                drilling, boring and flaring        riveting        
It also represent the higher cost and time in production terms.
The aviation evolution then relates to the use of new materials, such as the carbon fibre or the light alloys reducing weight, by making the aircraft high-performing.
The target is then to use the best techniques to reduce time by increasing quality.
The carbon fibre, indeed, represents a current topic and the solutions to improve the working thereof have a strong importance as the world industrial field needs innovation as response to quality, production time and thus cost reduction.
Such tool results to be “inventive” as it meets the market demands, by performing the drilling procedure with these qualities:                finished hole in one single pass (according to the aviation tolerances);        high useful life;        keeping the finished hole within the aviation tolerances for a guaranteed useful life;        high reduction in the operator's effort and therefore improvement in ergonomics;        possibility of performing drilling even on NC (numeric control) machines.        
Such procedures then have an important role in the productive process of assembling a plurality of components (portions), respectively jointed one another. In particular, the quality requested by the aviation procedures for the drilling working are very strict, therefore the resources to be used, both technological and human ones, must have high-performing features, with reference to the materials to be processed, and the hand tools to be used, such as for example the cutting tools dedicated to the various working to be performed. Another fundamental aspect relating the drilling process is the ever-increasing reduction in the working time and the useful life of the cutting tools. With specific reference to the aviation industry, wherein the decrease in weight and the increase in the used materials are searched for constantly, the composite materials assume ever-increasing importance and presence on the market.
With relation to the composite material the main features such as                High resistance;        High rigidity;        Lesser weight;        Long fatigue life;        Low thermal expansion;        High resistance to corrosion.        
Said features are increasingly higher than those of the traditional metallic alloys still used in the aviation industry. In contrast to all this, this material has a lot of difficulties in the drilling working with traditional techniques and tools indeed due to the above-mentioned high technical features.
Therefore the main need in the aviation industry is the high quality of the working to the performed (for example drilling, riveting, etc.) in particular on composite materials, such as made of carbon fibre and/or glass fibre, and/or light alloys (Aluminium) and/or Titanium alloys and/or plastic materials.
The drilling is surely the most difficult and important process in the working of the composite materials. Therefore, it requires a specific equipment varying depending upon the shape and the sizes of the portions, if it is a half-assembled one or it is a particular single one, they can be processed with hand equipment such as drills (Hand Tool) and dedicated hand tools existing in the working stations or on numeric control tool machines by means of a dedicated part-program. Another aspect to be considered is the huge quantity of drillings to be performed on each assembled piece, therefore a greater longevity of the cutting tools is requested so as to perform a lesser number of tool changes.
With the technology development, in particular in the aviation field, ever-increasing structural elements are made of composite material. It is further provided the assembly between elements for implementing “packets” of elements coupled therebetween, with high thickness. In particular, the present invention is directed towards the drilling of single or coupled therebetween structural elements (packets) such as: bulkheads and ribs with section shaped like “L” or “H” or “U”, longerons with section shaped like “Z”, and “L” and “U”, panels (skin) and reinforcements with single and double curvature.
The drillings of such packets are implemented, according to the project designs, by coupling elements made of the same material or elements made of different material. In the known art it is provided proceeding with the drilling of such packets by means of the technique of the subsequent passes, that is by proceeding to a sequence of drillings with various decreased diameters of the involved packet, spaced out by pauses to allow the cooling of the cutting tool and the stabilization of the material to be drilled, until implementing the hole with finished diameter. The cutting tools used in the known technique, in particular the so-called “lance-shaped points” have a reduced useful life, for example about 20 holes for drillings on CFRP-CFRP packets with thickness greater than 10 mm.
The most common drawbacks of drilling elements made of composite material are:                Surface delamination, FIG. 10/1, wherein the separation of the carbon ply is highlighted, due to the configuration of the cutting angles of the cutters of the lance-shaped point;        Breaking of the fibres, FIG. 10/2, wherein the breaking of the plies is highlighted, due to the cutters which do not have a suitable cutting angle;        Burnings of the inletting and outletting plies of the drilled element, FIG. 10/3, due to the heat accumulation of the cutting tool and to the high number of revolutions;        Ovalized hole, FIG. 10/4, due to the geometrical shape of the cutters of the cutting tool;        Poor duration of the tool due to the highly abrasive power of the material, in particular of the carbon-resin plies.        
Notwithstanding there is a particular tendency to implementing elements in composite material, in aviation field, even other types of materials, such as light alloys (Al) and titanium alloys (Ti) are used. Therefore, the above-mentioned elements for example longerons, and/or bulkheads, and/or ribs and/or panels can be manufactured with the above-mentioned materials and they can be coupled by obtaining several combinations of packets both of the same type and not and different elements.
Therefore packets constituted by Aluminium/Carbon Aluminium/Titanium Carbon/Aluminium Aluminium/Aluminium etc. then alternated therebetween can be found.